1. Field of the Invention
Embodiments of the present invention relate to a media access control (MAC) protocol of a wireless local area network (WLAN), and more particularly, to a configuration of a frame for use in frame transmission based on uplink multi-user multiple-input and multiple-output (UL MU-MIMO) technology.
2. Description of the Related Art
Recently, in wireless communication systems, a multiple-input and multiple-output (MIMO) technology for transmitting and receiving data using at least two antennas is being generalized. A wireless local area network (WLAN) also enables at least two transmission antennas to be used from the Institute of Electrical and Electronics Engineers (IEEE) 802.11n standard. The IEEE 802.11n standard allows for use of up to four antennas, and the IEEE 802.11ac standard allows for use of up to eight antennas. For example, in a case of using a great number of transmission antennas, data transmission may be performed based on transmit beamforming technology, thereby improving a performance of signal reception.
For efficient use of frequency resources, the IEEE 802.11ac for which standardization is in progress may include downlink multi-user multiple-input and multiple-output (MU-MIMO) technology enabling an access point (AP) to simultaneously transmit beamformed data frames to a plurality of stations (STAs). Also, research is being conducted into uplink (UL) MU-MIMO technology enabling transmission of data frames to the AP from the plurality of STAs and reception of the data frames at the AP through being separated for each stream, to be conducted simultaneously.
FIG. 1 is a diagram illustrating an example of a protocol used to transmit data based on UL MU-MIMO technology according to a related art.
Since stations (STAs) transmitting data based on the UL MU-MIMO communication are to simultaneously transmit beamformed data frames, an AP may need to perform a process of providing notification on a time at which a transmission is initiated. The process may correspond to a UL MU request sequence of FIG. 1. When the process ends, the STAs may transmit the beamformed data frames after a predetermined period of time elapses. When the beamformed data frames are received from the STAs, the AP may transmit, to each of the STAs, an acknowledgement (ACK) frame or a block ACK (BA) frame which corresponds to an ACK sequence of FIG. 1. Depending on a necessity, a protection sequence for preventing channel accesses of other STAs included in a basic service set (BSS) may be performed before the UL MU request sequence.
To successfully receive the beamformed data frames simultaneously transmitted from the STAs to the AP, a temporal length, for example, a transmission time of the beamformed data frame transmitted by each of the STAs may need to be the same, an intensity of a received signal may need to be almost the same, and a number of spatial streams (Nss) used for a transmission of each of the STAs may need to be acknowledged.